This invention relates to refuse collection vehicles of the type having an arm that carries container grabbing mechanism that may extend from the body of the vehicle to grasp a container, hoist it and dump its contents into the collection vehicle body, and return the container to its original position, and more particularly to apparatus for preventing the arm from inadvertently drifting outwardly from the vehicle by locking the arm extension drive when the arm is fully retracted.
Refuse collection vehicles are known which have an arm selectively extendible from the body of the vehicle and having grabbing or grasping apparatus at the end of the arm remote from the vehicle for clamping firmly about a refuse container. Associated with the arm is means for lifting the end of the arm including the grasping apparatus for dumping the contents of the container into a hopper at the top of the vehicle body. Such vehicles, known in the art as side loaders, have the obvious advantage in that only one person, to wit, a driver is necessary to collect refuse from a substantial number of dwellings or the like. The means for extending the arm includes a hydraulic drive cylinder with an extendible piston rod which permits the arm to be extended up to approximately 8 feet from the body so that a refuse container may be picked up in tight or difficult locations such as on the sidewalk of a street where the refuse vehicle may be prevented from getting close to the sidewalk because of parked vehicles and the like. The arm may be retracted fully so that the grasping apparatus is disposed substantially within the lateral confines of the body of the vehicle or in close proximity thereto thereby permitting the vehicle to be driven at highway speeds when necessary, such as when traveling to a dump site or the like.
A potential problem associated with the extendible lift arm is that which may occur should there be a failure of the arm extension drive means, e.g. the extension cylinder, the hydraulic circuit therefor or the electrical circuit controlling the operation of the hydraulic system. In such a situation the vehicle may be stopped by the driver of the vehicle and manually positioned if the arm is extended far enough from the vehicle to be seen from the cab by the driver. However, if the arm is not extended far enough so as to be viewable by the driver, the driver may not be aware of such failure and may drive the vehicle at speeds or conditions that would be hazardous to life and property. For example, the arm may spring outwardly due to centrifugal force while the driver is turning a corner or driving at less than relatively high speeds on a street or at high speeds on a highway. Should the arm extend in this manner to its full length an obviously dangerous situation is presented.
This problem was set forth in Flerchinger and Smith co-pending U.S. patent application Ser. No. 08/661,197 filed Jun. 10, 1996, now U.S. Pat. No. 5,755,547, and assigned to the common assignee of the instant invention. There, the lift arm is carried by a carriage which is slidably mounted on a track and retaining apparatus is provided for locking the carriage and thus the arm in various positions less than the fully retracted position of the carriage. The retaining apparatus includes a keeper plate movable with the carriage and a latch for seizing and holding the keeper when the carriage is not being driven.
Other extendible lift arm refuse vehicles utilize mechanisms which pivot or swing the arm relative to a fixed frame mounted on the vehicle. Here, there is no slidable carriage. Hydraulic cylinders act to extend and pivot the arm. The prior art attempted to address the problem resulting from a failure of the extension cylinder or its control by four known methods. One method utilized a chain and pin arrangement wherein the chain was looped around the arm to keep the arm fully retracted. This required the operator to physically disembark from the vehicle to install the chain and pin. The second method utilized friction cams and roller detents. This technique however, has been unsuccessful since the detent or friction is readily overcome as the vehicle bounces along a roadway or turns about a curve. Hydraulic detents within the hydraulic drive cylinder have been utilized but are found to wear rapidly and are unreliable and no visual inspection of the cylinder may be made to determine whether the detent is functioning properly. A pilot operated hydraulic check valve or counterbalance valve on the hydraulic drive cylinder has been utilized and although this corrects for a leaky valve or broken hose, if the hydraulic drive cylinder piston fails the arm will extend from the vehicle.